It has long been known to make circular saw blades according to patents U.S. Pat. No. 1,723,843 and U.S. Pat. No. 2,013,943 with substantially radial slots, which may start at the inner or outer perimeter of the blade, or may be located wholly within the blade surface.
The main purpose of the slots is to avoid tangential stresses since tangential compressive stress at the outer perimeter or tangential tensile stress at the inner perimeter will make the saw blade liable to buckling or vibration even at low speed. Such buckling or vibration may also occur when the tooth area is heated in use.
To minimize the risk of fatigue cracks at the ends of the slots which may later spread to other parts of the blades, the ends of the slots are made with a shape to lower the stress concentration factor, such as round holes with a diameter larger than the slot width as in U.S. Pat. No. 1,723,843, or narrow curved cutouts continuous with the straight slot and curving more than half a circle according to the patents DE 32 32 778 and DE 33 30 956.
The detailed shape of the slots can be varied to influence the generation and damping of noise. In an idling saw blade, the noise is mainly aerodynamic whistling in the slots and the gullets between teeth. To minimize whistling, the volume of the gullets and slots should have a small volume, and the stress lowering holes can be filled with some deformable substance as shown in U.S. Pat. No. 3,981,216. The slots can be positively inclined to avoid additive coupling between the gullet whistling and the slot whistling according to U.S. Pat. No. 1,723,843, or negatively inclined to avoid sawdust sticking in the slots according to U.S. Pat. No. 3,981,216.
An active vibration damping can be achieved by making slots with zero width according to U.S. 2,013,943, letting the sides of the slots rub against each other when the blade vibrates, but then the main function of avoiding tangential stress is impaired. It has also been suggested in DE 33 10 247 to let the slot width decrease to zero at its end, locating an open hole some distance from the slot end to catch any crack before it spreads, but since the crack direction is not determined there is still a great risk of spreading to other parts of the blade.
The present invention relates to a saw blade with a type of slot which avoids tangential stresses without the risk of cracks spreading, and which lowers the noise level to low volume by active damping through a previously not utilized effect.